Data may be transmitted between devices using many signaling protocols. According to a simultaneous bidirectional signaling protocol, a first device transmits signals to a second device over a signal line and also receives signals from the second device over the signal line. Since the same signal line carries both signals, each device requires a technique to distinguish the signal transmitted by the device from the signal transmitted to the device.
A device may distinguish a first signal transmitted by the device from a second signal transmitted to the device by subtracting the first signal from a composite signal that is present on the signal line. According to this technique, the device receives the composite signal from the signal line, subtracts a duplicate version of the first signal from the composite signal using capacitor-based subtraction circuits, and outputs the result of the subtraction. The result is intended to be substantially identical to the second signal transmitted to the device.
However, the above-mentioned capacitor-based subtraction circuits yield approximately 6 dB of attenuation and are often unable to operate at desired data rates.